This invention relates to an improvement of a ceramic precombustion chamber for an internal combustion engine such as a diesel engine.
In order to improve heat-resistance and thermal efficiency of internal combustion engines, it has been widely used to make precombustion chambers by a ceramic body as disclosed in Japanese Patent Application Laid-open No. 62-10,418. Such a ceramic precombustion chamber is usually made of upper and lower ceramic bodies fitted in a metal ring by thermal shrinkage fit for the convenience in manufacture. However, as thicknesses of walls forming a vortex chamber at a lower portion of the ceramic bodies are not uniform, surface pressures on the ceramic bodies caused by the thermal shrinkage fit are uneven. As a result, there is a tendency of cracks to occur in curved portions between a bottom wall and side walls of the lower portion of the ceramic bodies.